The present invention relates to a method for fabricating a semiconductor device; and, more particularly, to a method for depositing a metal film used as an electrode of a high dielectric capacitor and a ferroelectric capacitor in a dynamic random access memory (DRAM) and a ferroelectric random access memory (FeRAM) device.
Generally, a chemical vapor deposition (CVD) process is used to deposit a thin film on a substrate such as an exposed surface of a wafer and a silicon wafer. A precursor used in the CVD process is a thermally decomposable volatile mixture contacting to a substrate heated above a decomposing temperature of the precursor. A layer deposited in accordance with the CVD process, e.g., a layer constituted with metal, a metal mixture, metal-alloy, ceramic, a metal compound or a mixture of the above materials is deposited on a substrate depending on a selection of the precursor and a reaction condition.
It is known that a Ru thin film formed through an integration process, particularly, the CVD process has excellent electric conductivity, high stability at a high temperature range and good adhesiveness with silicon, silicon oxide and ceramic oxide.
The Ru thin film is used as an electrode or a wiring material of a capacitor in a dynamic random access memory (DRAM) and ferroelectric random access memory (FeRAM) device with giga bites. Since the Ru thin film is nearly non-reactive with silicon or metal oxides, it is possible to be used as a barrier against silicon or oxygen. Also, the Ru thin film can be used as a catalyst for high polymer synthesis.
Currently, there have been various studies on precursors of Ru used in the CVD process for depositing the Ru film.
The following will describe the CVD process for depositing the Ru film in accordance with a prior art.
RuXn is a precursor compound of the Ru used in the CVD process for a typical Ru film deposition. With use of O2 gas as a reaction gas, the Ru film is deposited based on the following reaction equation.
RuXn+O2xe2x86x92Ru+reaction productxe2x80x83xe2x80x83Equation 1 
However, there are problems in the prior art. First, there occurs the agglomeration phenomenon during a thermal process due to a low density of the Ru film. The Ru film is deposited at a temperature ranging from 250xc2x0 C. to about 350xc2x0 C. Because the Ru is deposited at a low temperature and impurities are included in the deposited Ru film due to this low deposition temperature, the Ru film has a decreased density. It is necessary to treat the Ru film with a high thermal process. However, there occurs severe agglomeration phenomenon as the Ru film is crystallized during the high thermal process.
Continuous to the first explained problem, O2 gas employed as the reaction gas in the CVD process is contained within the Ru film and oxidizes a bottom layer, e.g., a diffusion barrier layer applied on between a plug and a bottom electrode. Although the reaction gas is O2, which is an oxidizing gas, the Ru film is reduced and deposited as a metal layer. Therefore, the reaction between the Ru precursor and the O2 gas become very complex, and large amounts of impurities, particularly O2, remain within the deposited layer.
The O2 included in the Ru film is eventually diffused and oxidizes the diffusion barrier layer such as a TiN layer, thereby reducing electric properties.
Third, the Ru precursor is decomposed in a vapor phase, and subsequently a particle is generated. Since the Ru precursor strongly reacts with the O2 gas in a vapor phase, there occurs vapor decomposition before reaching to a substrate. Due to this vapor reaction, volatile materials, mainly carbonates and oxides, are formed on top of the Ru film in cluster forms. These volatile materials become a main factor for generating the particle.
It is, therefore, an object of the present invention to provide method for depositing a metal film capable of suppressing oxygen from being remained within the deposited film and preventing clustering of the metal film due to a low thermal deposition by employing a chemical vapor deposition (CVD) process and a method for depositing particularly a Ru film by using the same CVD process.
It is another object of the present invention to provide a method for forming a capacitor capable of preventing a bottom layer of the Ru film from being oxidized when depositing a bottom electrode with use of the Ru film.
In accordance with an aspect of the present invention, there is provided a method for depositing a metal film by using a chemical vapor deposition process, including the steps of: loading a substrate to a reactor where a metal film will be deposited; heating the substrate to densify the metal film as simultaneous to a deposition of the metal film; and depositing the metal film on the substrate by adding a precursor of the metal film and a reaction gas having a reducing ability to the heated substrate.
In particular, the substrate at the step of heating the substrate is heated to a temperature ranging from about 350xc2x0 C. to about 900xc2x0 C. Also, the metal film is any one selected from a group consisting of Ru, Fe, Os, Co, Rh, Ir, Ni, Pd and Pt.
In accordance with another aspect of the present invention, there is also provided a method for forming a capacitor, including the steps of: forming an inter-layer insulating layer on a substrate; forming a connection pattern stacked sequentially of a plug contacting to the substrate by passing through the inter-layer insulating layer and a diffusion barrier layer; depositing a metal film for a bottom electrode on the connection pattern by employing a chemical vapor deposition process with use of a reductive reaction gas so to perform the deposition and densification of the metal film simultaneously; and forming sequentially a dielectric layer and a top electrode on the metal film.
In addition, the step of depositing the metal film is proceeded at a temperature ranging from about 350xc2x0 C. to about 900xc2x0 C. Furthermore, the reaction gas having a strong reducing ability is any one selected from a group consisting of NH3, H2, hydrazine (N2H4), Me2NNH2, NH2R, NHR2, NR3, alkyl hydrazine having about 1 to 10 carbon branches, dialkyl hydrazine having about 1 to 10 carbon branches and a mixed gas of the above substrates. Meanwhile, the R is any one selected from a group consisting of H2, alkyl having about 1 to 10 carbon branches, alkenyl having about 1 to 10 carbon branches, alkoxy having about 1 to 8 carbon branches, aryl having about 6 to 12 carbon branches and a derivative of the above substrates added with one of halogen elements.